Both clinical and experimental observatons indicate that the cerebellum plays a critical role in the initiation of voluntary movement and in the control of its force and velocity. The exact nature of that control, however, is not known. It is not known whether the cerebellar output specifies or facilitates the force used to maintain the position of a body part or the movement of that part, or whether it specifies aspects related to displacement variables, with the forces required to achieve position maintenane or a displacement being computed elsewhere in the central nervous system. It is also not known what role static and dynamic sensory feedback to the cerebellum plays in the formulation of the cerebellar output associated with movement. It is proposed that some light can be shed on these questions through the method of recording the spike activity of single cerebellar output neurons during the repetitive performance of position maintenance and simple voluntary movements by experimental animals (cats). A method has been devised whereby the force and displacement parameters of these functions can be separately compared with the tonic and phasic discharge pattern of interpositus and dentate neurons. An attempt will also be made to examine how dynamic sensory feedback from the moving limb influences the discharge patterns of neurons whose activity appears related to some aspect of the movement.